LANbada for SAA Theory of Operation

Overview

On a PC with a complete installation of IBM's PC Support, there are a number of "layers" of hardware and software that lie below the surface of the application seen by the user. For example, there is the physical hardware connection to the AS/400, the appropriate drivers to communicate with that hardware, and the APPC router. The APPC (Advanced Program-to-Program Communication) router is the key component that interprets calls made by client applications (such as Rumba, Work Station Function, File Transfer, or Shared Folders) and passes them on to the driver for transfer to the host. These layers impose quite a resource burden on the PC.

LANbada for SAA uses these same components, but minimizes overhead and maximizes utility by sharing these components among many users. Here's how it works: the LANbada for SAA gateway PC contains the hardware and software necessary to conduct APPC conversations with an AS/400. Running over the APPC router, however, is the LANbada for SAA gateway software instead of client applications. The gateway software then provides APPC router access to client applications running on LAN-based PCs. Click here to see a diagram of this structure. (13537 bytes)

On each LAN PC, the LANbada for SAA network router software (DOS or Windows version) is executed. This network router communicates with the gateway on one side, and with client applications on the other. Client applications are unaware that they are interfacing with a "dummy router" instead of the actual APPC router. Note that this LAN-based approach eliminates the need for the complex LLC protocol stack, a source of frustration at many PC Support installations.

Thus, the gateway and network router together act as a transparent "bridge" between client applications running on multiple LAN-based PCs and the AS/400 host. See the accompanying diagram for an illustration of this architecture.

An added advantage of this approach is that the AS/400, too, requires fewer resources. This is because instead of having to open a separate APPC channel to the AS/400 for each PC (as is usually the case), only one is required for all users.

System Components

The system is composed of three main components: the gateway, DOS network router, and Windows network router.

LANbada for SAA Gateway

The LANbada for SAA gateway consists of a Setup program, the gateway itself, and a monitor utility. Setup is used to define the gateway name, network type, maximum sessions, and other parameters. The heart of the system is the gateway which acts as a transparent bridge between the APPC router and the network (see diagram, previous page). Because the gateway PC can be configured with any APPC connection type (Twinax, SDLC, Async, Ethernet, or Token Ring), LANbada for SAA is completely hardware-independent. The monitor utility provides realtime data on the active gateway, users, and applications, and can be used to disconnect particular workstations from the gateway.

The gateway is available in different versions supporting different numbers of sessions: 8, 16, 32, and 64. Sessions taken by one user are removed from the session pool available to all users. Because IBM's PC Support router only supports a maximum of 32 sessions, the 64-session version of LANbada for SAA utilizes a custom-designed router, available exclusively for Twinax connections. In addition to providing twice the number of sessions, this router provides a unique error- recovery feature--if communication between the gateway and AS/400 is lost for whatever reason, the gateway will continue attempts to reestablish communication. As soon as the connection is restored, the gateway makes all sessions immediately available without the need to reboot.

LANbada for SAA Network Router for Windows

The Windows network router is installed on each LAN user's PC. It is a full Windows sub-system (it does not require any DOS components to be installed on the PC) and consists of a Setup module and a Runtime module. Both are designed with a clear, user-friendly interface to accommodate all users. Users can configure their setup to automatically connect to particular gateways, or to all defined gateways, when they click the LANbada for SAA icon. When minimized, the icon is animated to show that gateway connections are active.

Once the network router is active, client software (not included with LANbada for SAA) such as BOSaNOVA Client or Wall Data Rumba can be started. The client software will operate as if it were on a PC running PC Support.

The Windows network router supports communication with multiple hosts, via multiple gateways (up to 32), even if different gateways are using different protocols (IPX and NetBIOS). Taking this one step further, the network router will even try to find available sessions at all gateways connected to a requested system without user intervention.

To APPC applications, the LANbada for SAA network router appears identical to a standard APPC router. When a client application sends APPC calls, the network router intercepts them and transparently routes them, via the network, to the real APPC router on the gateway.

LANbada for SAA Network Router for DOS

The DOS network router configures itself on each LAN user's PC as a PC Support replacement: client applications interact with it as if it were actually a PC Support router. As with the Windows version, the network router transparently handles all APPC calls by routing them to the gateway via the network.

An easy-to-use Setup program allows users to select the gateway to which they will connect. A DOS batch file, automatically created during installation, is used to start the router. All PC Support components and other APPC software will function as if the PC Support router itself was running, but with dramatically lower memory requirements.